The premise behind the French method of cooking en cocotte (or casserole roasting) is to slow down the cooking process in order to concentrate flavour.
Fish cooked for an extended period of time usually winds up dry, but a combination of low oven temperature, moist-heat environment, and the right cut of fish allows it to remain juicy and tender.
We found that meaty swordfish steaks were particularly well suited to cooking en cocotte. The fresh Mediterranean flavours of mint, parsley, lemon, and garlic easily combined with sliced cucumber to make an insulating layer on which to cook the fish; we then turned the cucumber mixture into a complementary flavourful topping for serving.
It is important to choose steaks that are similar in size and thickness to ensure that each piece will cook at the same rate. If swordfish isn’t available, you can substitute halibut.
SWORDFISH EN COCOTTE WITH SHALLOTS, CUCUMBER AND MINT
Start to finish: 1 hour
3/4 cup fresh mint leaves
1/4 cup fresh parsley leaves
5 tablespoons extra-virgin olive oil
2 tablespoons lemon juice
4 garlic cloves, minced
1 teaspoon ground cumin
1/4 teaspoon cayenne pepper
Salt and pepper
3 shallots, sliced thin
1 cucumber, peeled, seeded, and sliced thin
4 (4- to 6-ounce) skin-on swordfish steaks, 1 to 1 1/2 inches thick
Adjust oven rack to lowest position and heat oven to 250 F. Process mint, parsley, 3 tablespoons oil, lemon juice, garlic, cumin, cayenne, and 1/4 teaspoon salt in food processor until smooth, about 20 seconds, scraping down sides of bowl as needed.
Heat remaining 2 tablespoons oil in Dutch oven over medium-low heat until shimmering. Add shallots, cover, and cook, stirring occasionally, until softened, about 5 minutes. Off heat, stir in processed mint mixture and cucumber.
Pat swordfish dry with paper towels and season with salt and pepper. Place swordfish on top of cucumber-mint mixture. Place large sheet of aluminum foil over pot and press to seal, then cover tightly with lid. Transfer pot to oven and cook until swordfish flakes apart when gently prodded with paring knife and registers 140 F, 35 to 40 minutes.
Carefully transfer swordfish to serving platter. Season cucumber-mint mixture with salt and pepper to taste, then spoon over swordfish. Serve.